154 ANATINID^. 



radiately ? sometimes partially) striated or suleated. Onlj' 

 palaeozoic species are referred to the genus ; some of them are in 

 external form almost identical with Pharella, and it as yet 

 remains to be shown whether there are in Sanguinolites an}'- 

 hinge-teeth or not. In the Brit. Pal. foss. (p. 276), M'Coy con- 

 siders this genus apparently identical with King's AUorisma, 

 which is very doubtful. 



POMACRUs, Meek, 1811. Shell thin, more or less elongate- 

 subtrapeziform, nearly or quite equivalve, either inequilateral 

 or equilateral, the beaks being nearer the anterior or posterior 

 end, or central, according to the species ; valves closed all 

 around, and each with a well-defined keel or more obtuse 

 ridge extending from the posterior side of the beaks to the 

 posterior basal extremity ; anterior side attenuated and pro- 

 duced ; posterior margin wider (higher) than the other, and 

 obliquely truncated ; dorsal margin sloping in front of the beaks, 

 and more nearl}^ horizontal and appai'ently without an escutcheon 

 behind them ; ligament external or marginal, rather long ; surface 

 with concentric lines and ridges, and sometimes obscure radiating 

 markings on the umbonal region. Hinge, muscular, and pallial 

 impressions unknown. P. nasutus ^Meek. 2 sp. Carb. ; Missouri. 



Pyanomya, Miller, 1882. 



Distr. — P. gibbosa, Miller (cxx, 9, 13)., Hudson Riv. Group; 

 Cincinnati, Ohio. 



Shell small, inequilateral, with thin, fragile, ventricose, edentu- 

 lous valves, united by an external ligament ; no escutcheon. 



GrRAMMYSiA, de Yemeuil, 1841. 



Distr. — Silur., Devon. ; N. Am., Eur. G. pes-anseris, Sandb. 

 (cxx, 14). G. ovata, Sandb. (cxxi, 5). 



Shell equivalve, inequilateral, transverse; not gaping; mus- 

 cular impressions very unequal; pallial line posteriorly rounded, 

 bordering the large muscular impression so as to leave the latter 

 two-thirds without it ; ligament exterior, prolonged, in a depres- 

 sion of the dorsal line ; surface with one or more oblique ribs, 

 and several rounded concentric plications. 



Orthonota, Conrad, 1841. 



Distr. — 0. undulata, Conr. 0. contracta, Conr. (cxxix, 13, 14). 

 L. Silur. ; F. S. 



Shell narrow, with subparallcl upper and lower margins, very 

 inequilateral, the beaks being subanterior and tumescent, lunula 

 in front of the beaks somewhat excavated, very thin, surface pos- 

 teriorly generally undulately striated, hinge apparently without 

 teeth. 



